Pressure-cap assembly for terminal bushings



April 13, 1965 J. H. FRAKES ET AL CAP ASSEMBLY FOR TERMINAL BUSHINGS PRESSURE- Filed. April 30, 1962 4% a. K). a 7

United States Patent C 3,178,504- PRESSURE-CAP ASSEMBLY FGR TERMENAL BUSHENGS James H. Brakes, Penn Hiils, mil Clidord' A. Bridges,

Hempfield Township, Westmoreiand @ounty, Pa, assignors to Westinghouse Electric (Jorporation, East Pittsburgh, 1 2., a corporation of Pennsyivanra Filed Apr. 30, 1962, Ser. No. 191,234 6 Claims. (Cl. 174-12) This invention relates to pressure-cap assemblies for terminal bushings in general, and, more particularly, to an improved construction of a pressure-cap assembly for a terminal bushing involving few parts and adapted for ready assembly.

A general object of the present invention is the provision of an improved pressure-cap assembly for a terminal bushing, involving a minimum of parts, resulting in a leak-tight construction, and moreover permitting an effective copper-to-aluminum connection, when desired.

A more specific object of the present invention is the provision of an improved pressure-cap assembly for a terminal bushing, in which the associated terminal stud may be threadedly secured within the outer extremity of the axially extending tubular conductor stud without a brazing or a soldering connection.

Further objects and advantages will readily become apparent upon reading the following specification, taken in conjunction with the drawings, in which:

FIG. 1 is an end elevational view of a three-pole sulfurhexafiuoride (SP gas-type of circuit interrupter, to indicate the general type of apparatus, with which the improved pressure-cap assembly of the present invention may be employed; and,

FIG. 2 is an enlarged, partially vertical sectional view taken through the improved terminal bushing structure of the present invention with nonessential portions broken awa R ferring to the drawings, and more particularly to FIG. 1 thereof, the reference numeral 1 generally designates an electrical apparatus, such as a circuit interrupting structure, involving a tank structure 2, with hinged end caps 3, 4, out of which may be laterally pulled a circuit interrupting assembly 5, which is preferably supported at the lower end of terminal bushings 6, '7. Disposed at the upper end of the tank structure 2 is a pair of cylindrical support cylinders 11, 12, having upper perforated sup port plates 8, to which a grounded mounting flange plate 9 (FIG. 2) of each terminal bushing 6, 7 may be secured, as by bolts 9a.

It will be observed that the cylindrical support portions 11, 12 are Welded, as at 13, to the upper-side of the tank structure 2. Preferably, sulfurhexatluoride (SP gas It), at a pressure of say 60 p.s.i., is disposed within the tank structure 2. In addition, a high-pressure storage tank, not shown, is associated with the right-hand end of each arc-extinguishing assemblage 5, as viewed in FIG. 1, and serves the purpose of releasing a blast of gas during the interrupting operation, which is subsequently exhausted into the general interior 15 of the tank structure 2, as set forth in more detail in United States patent application filed January 23, W59, Serial No. 788,668, now United States Patent 3,057,983, issued October 9, 1962 to Benjamin P. Baker, Russell N. Yeckley and Joseph Sucha, and assigned to the assignee of the instant application.

With reference to FIG. 2, which shows in more detail the pressure-cap assembly associated with the terminal bushing 7, it is apparent that a tubular metallic conductor stud 14 extends axially through the terminal bushing '7, and is in gas communication with the interior 15 of the tank structure 2. As previously mentioned, the

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ground-flange assembly 16 of the terminal bushing 7 is preferably connected by the bolts 9a to the perforated support plates 8.

With reference to the upper portion of FIG. 2 of the drawings, it will be noted that the tubular conductor stud 14 has the upper interior portion 14a thereof threaded, so as to threadedly receive a solid terminal stud 18, to which a line connection L may be made, as well understood by those skilled in the art.

Threadedly secured to an intermediate portion 18a of the terminal stud 18 is a spring support collar 29 bearing upon a gasket 21. The annular gasket 21, in turn, abuts a shoulder portion 22 of an annular spring seat 23, the latter serving as an upper seat for a plurality of annularly-disposed helical compression springs 24.

As shown in FIG. 2, the lower ends of the plurality of coil springs 24 seat upon a lower spring seat 25, which, in turn, bears upon a cup-shaped cap bowl 2s. In addition, a gasket 27 is preferably provided between the upper extremity 28 of the upper external weatherproof insulator shell 29 and the lower portion of the cap bowl 26 to provide a gas-tight connection therebetween.

The gasket 21 prevents the existence of a shunt current path in case of contact between the tubular conductor stud M- and the spring seat 25. Such a shunt circuit. might cause current flow through high-resistance parts and consequent heating.

As well known by those skilled in the art, the compression springs 24 maintain axial compressive force upon the weatherproof shells 29, 42 and the interposed ground flange assembly 16, thereby insuring maintenance of the several gaskets 27 under pressure for a leak-tight construction. On the other hand, the terminal stud 1S and the tubular conductor stud 14 are correspondingly maintained under tensile load, and this insures a good current-carrying engagement between the threaded surfaces of the component parts 14, 13.

A perforation 38 is provided in the side wall of the conductor stud 14 to permit gas, such as sulfurhexafiuoride (SP gas Iii, to flow upwardly through the tubular conductor stud 14- in the diretcion indicated by the arrow 31, through the aperture 39 and into the interior 32 of the bushing cap assembly 33. As shown in FIG. 2, the upper peripheral portion 26a of the cap bowl 26 has secured thereto a flexible annular closure member 37, which may flex in response to diiferential elongation of the tubular conductor stud 14 and the porcelain shells 29, 42 of the terminal bushing 7.

The inner peripheral portion 37a of the flexible closure member 37 is preferably soldered to a support collar 45, which, in turn, is threadedly secured to the solid terminal stud 18, as shown.

The pressure-cap assembly 33 of the present invention has a number of important advantages over previous prior art constructions. First, the arrangement eliminates any casting being responsible for gas containment, thereby preventing gas leakage due to cast metal porosity. Sec ondly, in the pressure-cap construction 33, the solid terminal stud 18 and the tubular conductor stud 34- are threadedly engaged. With this joint being subjected to high tensile load, a current path is maintained without resorting to a brazing or soldering connection. Joining these parts 14, 18 without brazing or soldering permits the use of aluminum for the tubular conductor stud 14 for bushings of suitable current ratings. The terminal stud 18, which is exposed to the atmosphere, extends through the top of the cap 33 and is preferably made of copper. Moreover, the threaded joint being inside the cap 33 need not be gas-tight. The construction of the improved pressure cap assembly 33 permits the use of greater conductor cross-sectional area for additional current-carrying capacity inside of the cap 26, where the ea /"sens.

heating eliect may be greatest due to the annular cluster of magnetic springs 24. This results from the extraction of heat by conduction to the terminal stud 13.

Although there has been illustrated and described a specific structure, it is to be clearly understood that the same was merely for the purpose of illustration, and that changes and modifications may readily be made therein by those skilled in the art, without departing from the spirit and scope of the invention.

We claim as our invention:

1. in combination, a gas-filled terminal bushing including a pair of axially-extending insulator shells and an interposed ground-flange assembly, a tubular conductor stud extending through the pair of insulator shells and adapted for transmitting gas from an associated gasfilled casing containing electrical equipment into the bushing interior, the outer end of the tubular conductor stud being internally threaded, a pressure cap assembly having a cap bowl and including a solid terminal stud extending into the cap bowl and threadedly secured within the internally threaded portion of the tubular conductor stud, a pair of spaced annular spring seats, one of said annular spring seats being disposed adjacent the end of one of said insulator shells and substantially adjacent the internally threaded end of the tubular conductor stud and the other annular spring seat being disposed at a predetermined position along the length of the solid terminal stud, a plurality of circumferential]y-disposed compression springs interposed between said pair of annular spring seats and bearing thereon, a spring support collar threaded on an intermediate portion of said solid terminal stud and disposed on the opposite side of said other annular spring seat from said compression springs to resist outward spring force exerted thereon, the spring support collar having its position adjustable and permitting tension of said compression springs to be adjusted without requiring movement of the cap bowl of the pressure cap assembly with respect to the adjacent end of said one insulator shell.

2. The combination of claim 1 wherein insulating gasket means is interposed between said spring support collar and said other annular spring seat to prevent current flow therebetween.

3. A terminal bushing including at least one insulator shell, an axially-extending tubular conductor stud passing through said shell and having a portion of oneend thereof internally threaded, a pressure-cap assembly surrounding the extremity of the threaded end of said tubular conductor stud and having a solid threaded terminal stud extending thereinto and threaded into said tubular conductor stud, one end of the pressure cap assembly being adjacent the end of the insulator shell, a pair of annular spring seats in the pressure cap assembly, one of said annular spring seats being adjacent said one end of the pressure cap assembly and the other annular spring scat being disposed at a predetermined position along the length of the solid terminal stud, a plurality of circumferentially-disposed compression springs interposed between said pair of annular spring sea-ts'and tending to force the other annular spring seat outwardly, a springsupport collar threaded on an intermediate portion of said solid terminal stud and disposed outwardly of said other annular spring seat from said compression springs and resisting the outward force exerted thereon, the spring support collar having its position adjustable and permittin the tension of the compression springs to be adjusted without requiring movement of the pressure cap assembly with respect to the adjacent end of the insulator shell.

4. The combination of claim 3, wherein gasket means is interposed between said other annular spring seat and said spring-support collar to prevent current flow therebetween.

5. The combination of claim 1, wherein an additional support collar is threaded on the solid terminal stud between the spring support collar and the outer end of the solid terminal stud, and a flexible closure member of the pressure-cap assembly is secured thereto.

6. The combination of claim 3, wherein the pressurecap assembly includes a cap bowl, an additional support collar is threaded on a portion of the solid terminal stud between'the spring support collar and the outer end i of the solid terminal stud, and a flexible closure member closing the cap bowl is secured to said additional support collart References Cited by the Examiner UNITED STATES PATENTS 2,285,594 6/42 Lingal 174l2 2,459,612 1/49 Baker 174l42 X 3,059,044 10/62 Friedrich et. al 174-l8 JOHNS F. BURNS, Primary Examiner.

JOHN P. WILDMAN, Examiner. 

3. A TERMINAL BUSHING INCLUDING AT LEAST ONE INSULATOR SHELL, AN AXIALLY-EXTENDING TUBULAR CONDUCTOR STUD PASSING THROUGH SAID SHELL AND HAVING A PORTION OF ONE END THEREOF INTERNALLY THREADED, A PRESSURE-CAP ASSEMBLY SURROUNDING THE EXTREMITY OF THE THREADED END OF SAID TUBULAR CONDUCTOR STUD AND HAVING A SOLID THREADED TERMINAL STUD EXTENDING THEREINTO AND THREADED INTO SAID TUBULAR CONDUCTOR STUD, ONE END OF THE PRESSURE CAP ASSEMBLY BEING ADJACENT THE END OF THE INSULATOR SHELL, A PAIR OF ANNULAR SPRING SEATS IN THE PRESSURE CAP ASSEMBLY, ONE OF SAID ANNULAR SPRING SEATS BEING ADJACENT SAID ONE END OF THE PRESSURE CAP ASSEMBLY AND THE OTHER ANNULAR SPRING SEAT BEING DISPOSED AT A PREDETERMINED POSITION ALONG THE LENGTH OF THE SOLID TERMINAL STUD, A PLURALITY OF CIRCUMFERENTIALLY-DISPOSED COMPRESSION SPRINGS INTERPOSED BETWEEN SAID PAIR OF ANNULAR SPRING SEAT AND TENDING TO FORCE THE OTHER ANNULAR SPRING SEAT OUTWARDLY, A SPRINGSUPPORT COLLAR THREADED ON AN INTERMEDIATE PORTION OF SAID SOLID TERMINAL STUD AND DISPOSED OUTWARDLY OF SAID OTHER ANNULAR SPRING SEAT FROM SAID COMPRESSION SPRINGS AND RESISTING THE OUTWARD FORCE EXERTED THEREON, THE SPRING SUPPORT COLLAR HAVING ITS POSITION ADJUSTABLE AND PERMITTING THE TENSION OF THE COMPRESSION SPRING TO BE ADJUSTED WITHOUT REQUIRING MOVEMENT OF THE PRESSURE CAP ASSEMBLY WITH RESPECT TO THE ADJACENT END OF THE INSULATOR SHELL. 